"Princesses exist" is not a trope on their own. You may be looking for one of the following:
- Good Princess, Evil Queen — the (usually) younger and more beautiful princess is morally superior to the older and often less attractive Queen.
- Gratuitous Princess — princesses exist in a setting or culture that doesn't actually have royalty, or when there are more princesses than plausible in the setting (e.g. having an entire school of princesses).
- Honorary Princess — the character is not a princess, but is referred to as such to show off her distinguished status.
- Princess Protagonist — the lead character is a princess, because what little girl wouldn't want to imagine herself as one?
- Rags to Royalty — an everygirl is given the title of princess or is revealed to be the missing heir to a throne.
- Save the Princess — the Damsel in Distress is a princess because rescuing a kidnapped princess (and possibly winning her hand in marriage as a result) is so much more glamorous than saving Plain Jane.
For tropes about princesses in general, see Princess Tropes.
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